Giant planets could reach “maturity” much earlier than previously thought

The study reports the measurement of the masses of two giant planets that orbit the young solar-type star V1298 Tau,whose total lifetime is about 10 billion years. They were discovered in 2019 using data from NASA's Kepler space telescope, which allowed the measurement of their sizes, slightly smaller than Jupiter, and of their orbital periods, 24 and 40 days for V1298 Tau b and e, respectively.

“The characterization of very young planets is extraordinarily difficult,” says the first author of the study Dr Alejandro Suárez Mascareño from the Instituto de Astrofísica de Canarias (IAC). “The parent stars have very high levels of activity and until very recently it was unthinkable to even try”. He adds: “Only thanks to detections made with space telescopes, combined with intense radial velocity campaigns from Earth-based observatories and the use of the most advanced analysis techniques, it was possible to begin to see what is happening in such early stages of the evolution of planetary systems”. In fact, for the new measurements of the planetary masses, it was necessary to separate the signals generated by these planets from the signal generated by the star's activity, which is almost ten times larger. At this point, the specialisation of STELLA (STELLar Activity) comes into play. “With its large wavelength coverage from ultraviolet to infrared radiation at a high spectral resolution, STELLA can track the magnetic activity of a star,” adds Professor Klaus Strassmeier, director of the research branch Cosmic Magnetic Fields at AIP and PI for STELLA.

The study shows that the masses and radii of the planets V1298 Tau b and c are surprisingly similar to those of the giant planets of the Solar System or in other old extrasolar systems. These measurements, which are the first to be obtained of such young giant planets, allow scientists to test current ideas about the formation of planetary systems. “For many years, theoretical models have indicated that giant planets begin their evolution as bodies with a larger size, and that they later contract over hundreds of million or even billions of years,” explains Dr Víctor J. Sánchez Béjar, researcher at the IAC and co-author of the work. “We now know that they can actually reach a size similar to that of the planets in the solar system in a very short time,” he notes.

The study of young systems gives researchers clues about what happened during the infancy of our solar system. “We still do not know if V1298 Tau and its planets are a normal case and whether their evolution is similar to that of most planets or if we are facing an exceptional case; if this were the normal scenario, it would mean that the evolution of planets like Jupiter and Saturn could have been very different from what we think,” comments Dr Nicolas Lodieu, a researcher at the IAC, former PhD student at AIP and also a co-author of the work. The results of this work thus help to build a more solid idea of the early evolution of planetary systems like ours.

To achieve the measurement of these masses, the study has required a significant observational effort and the collaboration of multiple observatories and institutions from different countries. It was necessary to combine radial velocity measurements from various instruments such as the high-resolution HARPS-N ultrastable spectrograph at the Roque de los Muchachos Observatory's (ORM) Telescopio Nazionale Galileo (TNG); the CARMENES high resolution spectrograph at the Calar Alto observatory; the HERMES spectrograph on the Mercator telescope, also at the ORM; and the SES spectrograph at AIP’s STELLA telescopes at the Teide Observatory. Observations taken from the Las Cumbres Observatory have been used to continuously monitor the variations of the star's activity.